|Publication number||US7418979 B2|
|Application number||US 11/655,446|
|Publication date||Sep 2, 2008|
|Filing date||Jan 19, 2007|
|Priority date||Jan 19, 2007|
|Also published as||US20080173367|
|Publication number||11655446, 655446, US 7418979 B2, US 7418979B2, US-B2-7418979, US7418979 B2, US7418979B2|
|Inventors||Thomas Joseph Keyes|
|Original Assignee||Thermacor Process, L.P.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (6), Referenced by (12), Classifications (13), Legal Events (4)|
|External Links: USPTO, USPTO Assignment, Espacenet|
1. Field of the Invention
The present invention relates generally to an apparatus and method for preventing disbondment in a bonded foam insulated piping system of the type used for conveying high temperature fluids.
2. Description of the Prior Art
Insulated pipelines are needed in a variety of situations. For example, distributed HVAC (heating, ventilation, and air conditioning) applications utilize chilled water for cooling and steam for heating. The chiller and boiler are typically contained in a central location and the chilled water and steam are distributed to other locations. For example, on a school campus the chiller and boiler may be located in a power plant building. The chilled water and steam are distributed to classrooms in separate buildings. A set of insulated pipelines is used to convey the chilled water from the chiller to other locations and back to the chiller. Another set of insulted pipelines is used to carry the steam from the boiler to the other locations and back to the boiler. Oftentimes, the temperature inside the pipe is either higher or lower than the ambient temperature surrounding the pipe. It is necessary for the pipes to be insulated in order to retain the internal temperature of the fluids and keep heating and cooling losses at a minimum. The insulated pipelines are usually located underground.
Insulated pipe of the type under consideration is conventional and commercially available. There are predominately two types of piping systems in use: Class-A drainable dryable testable (DDT); and polyurethane or polyisocyanurate bonded foam systems. The present application is directed toward the bonded foam type system. These systems utilize a steel pipe to convey fluid, and often the fluid is a different temperature as compared to the ambient environment. Around the outside of the steel pipe is a layer of insulating foam such as, for example, polyisocyanurate foam. In the case of high temperature piping systems, the insulating foam serves to keep heat loss from the starting location of the pipeline to the ending location at a minimum. Around the outside of the foam is a thin jacket of thermoplastic material, such as high density polyethylene (HDPE). The plastic jacket protects the foam from mechanical damage and also provides a watertight seal to prevent corrosion of the steel pipe. Although steel is commonly used for the inner pipe which carries the media to be piped, copper, aluminum or other metals as well as fiberglass, PVC, and similar materials may be utilized, as well.
The most important engineering criteria for a foam system of the type under consideration is that it must be treated as a bonded system. In other words, the foam is bonded to both the carrier pipe and the outer jacket. In such a case, the bonded system acts as a monolithic unit moving underground. Higher temperatures can act adversely upon the bonded foam system, however. The hot fluid in the steel carrier pipe causes the carrier pipe to thermally expand. At temperatures of 400° F. this expansion is on the order of 2.8 inches per 100 feet of pipe. This expansion is not a problem as long as the system remains bonded and the carrier pipe, foam and jacket move together as one unit underground. This movement is controlled by the expansion force of the steel carrier pipe, but it is the bond strength of the foam to the pipe and jacket that is important in keeping the system moving together. This monolithic movement of the system occurs along each incremental length of a particular run, and as long as total movement is not greater than 4 to 6 inches and the system remains bonded, no undue stress is subjected at any one point of the jacket. If the system were to disbond, however, the surrounding soil would fix the jacket in place and the carrier pipe would still thermally expand thereby pushing through and destroying the jacket at the first change of direction.
Generally speaking, the proper choice of insulating materials can counteract many of the thermal expansion effects discussed above. It has been well established by industry case history that the polyurethane foam bond for systems running at 250° F. to 300° F. is strong enough to keep the entire system acting as a bonded system. However, for systems running above these temperatures a higher temperature rated foam, such as polyisocyanurate foam, is generally required. Even in systems utilizing “high temperature” polyisocyanurate foam, the higher heat can, in some instances, begin to fry the foam at the foam/carrier pipe interface, thereby bringing into question the strength of the foam bond to the steel carrier pipe.
Various approaches have been taken to control this undesirable expansion in insulated pipe systems of the type under consideration. For example, expansion “bolster” materials are supplied in the form of resilient pads which can be used at elbows or expansion loops. These pads are placed adjacent to the piping and create a cushion which acts as a stress relief area in critical areas, such as angles and elbows.
Despite the advances seen in the high temperature piping industry, a need continues to exist for improved systems for preventing disbondment in bonded foam insulated piping systems.
A need also exists for such an improved system which utilizes many of the conventionally available materials and manufacturing techniques commonly used in the industry.
A need also exists for such a system which is simple in design and economical to implement.
The method and apparatus of the present invention provide an improved insulated piping system for conveying high temperature fluids. The insulated piping system has a first and second length of insulated and jacketed pipe, each having a joining end to be joined to an end of the other length, and each pipe length comprises an inner carrier pipe having an interior surface and an exterior surface. An envelope of foamed insulation surrounds the inner pipe exterior surface, and an outer protective jacket surrounds the envelope of insulation. The joining ends of adjacent pipe lengths are welded together to form fixed joints, whereby the adjacent pipe lengths provide a continuous length of fluid conduit for conveying high temperature fluids.
In addition, a discrete length of an external slip wrap is placed at a selected location along the length of the piping system, generally in a location at which the piping encounters an angular change of direction, such as at an elbow or expansion loop. The slip wrap comprises a loosely received outer sleeve for the piping which surrounds the outer protective jacket without being bonded thereto, whereby the insulated and jacketed pipe can move axially relative to the slip wrap for a selected distance once the pipe is buried in the ground. Preferably, the external slip wrap is a thin sleeve formed of a flexible plastic type material, such as a polyolefin material having characteristic coefficient of friction which allows the jacketed pipe to slide within the sleeve. In one preferred form of the invention, the external slip wrap may be formed of polyethylene.
The location of the slip wrap along the length of piping is selected to in order to prevent disbondment of the foam insulation from the inner carrier pipe. Prevention of disbondment is possible by allowing relative movement of the pipeline relative to the surrounding earth, thereby eliminating the separation of the envelope of foamed insulation from the exterior surface of the inner metal pipes as the temperature of the inner metal pipes increase and the pipeline expands. In a typical case, the lengths of insulated piping are part of a pipeline conveying steam, hot water or other hot fluids at a temperature in the range of above about 200° F.
Additional objects, features and advantages will be apparent in the written description which follows.
Turning first to
The piping systems of the type illustrated in
In the piping system illustrated in
The present invention is intended to provide a solution for possible disbondment problems for foam bonded piping systems that are operating at temperatures generally above about 200° F. At temperatures that begin to exceed 250° F., foams have been developed that are stable structurally to handle these higher temperatures, but the bond strength of the foams at these temperatures may come into question. The invention is intended to prevent the potential problems that might occur if the foam bond strength is not sufficient to cause the systems to expand as one monolithic item.
The reference in this discussion to pipe “lengths” is intended to refer to standard available factory pre-insulated piping of the type previously described having an inner metal pipe surrounded by an envelope of foamed insulation, which in turn, is contained within a polyolefin jacket. As referred to briefly above, typical commercial practice involves the use of steel, copper, aluminum or alloy conveying pipes, open or closed cell polyurethane, polyisocyanurate, polystyrene or the like, foamed rigid insulation and polypropylene, polybutylene, polyethylene, polyvinylchloride and similar protective jackets.
The present invention is an improvement to presently available pre-insulated piping of the type which is commercially available and familiar to those in the relevant industries. Prior art pipe lengths of this general type are commercially available as standard factory type product. For example, such products are available from Thermacor Process, LP of Fort Worth, Tex., assignee of the present invention. One typical example is sold commercially as the HT-406 High Temp Steel Piping System. The published specifications for systems are as follows:
diameter less than about 2″
A53 ERW Grade B, Std. Wt.
diameter greater than about 2″
A106 SML, Std. Wt. Black
Compatible with ASTM D3350
Specific Gravity (ASTM D792)
Tensile Strength (ASTM D638)
3100 psi min.
Elongation Ultimate (ASTM D638)
Compressive Strength (ASTM
2700 psi min.
Impact Strength (ASTM D256)
2.0 ft. lb/in. North Min.
Rockwell Hardness (ASTM D785)
D60 (Shore) min.
≦0.14 @ 70° F., ≦0.24 @ 406° F.
Closed Cell Content
≧2.5″ @ 366° F., ≧3.0″ @ 406° F.
The present invention addresses the problem of foam disbondment by helping insure that the inner carrier pipe and outer layer of bonded foam continue to move as a unit as the inner pipe expands. This object is accomplished by providing an “external slip wrap” which surrounds the outer protective jacket of the piping system at selected locations. The external slip wrap is a sleeve formed of a flexible polyolefin material having a desired characteristic coefficient of friction. Since the external wrap is not bonded to the protective jacket, the insulated and jacketed pipe can move axially relative to the slip wrap in the earth for a selected distance once the pipe is buried in the ground. It is important to note, the external slip wrap is not intended to further insulate or waterproof the piping system, as that is already handled by the foam and outer protective jacket respectively. Instead, the function of the external slip wrap is to allow movement of the insulated pipe by providing a slidable environment that normally would not exist when the surrounding earth is holding the protective jacket in place.
The external slip wrap of the invention is designated generally as 17 in
The preferred external slip wrap 17 of the invention is a thin sleeve formed of a flexible material, such as a suitable polyethylene material. As shown in
In the particular system illustrated in
However, because the external slip wrap allows the insulated and jacketed pipe to move axially relative to the wrap for a selected distance once the pipe is buried in the ground, the outer jacket remains intact and the integrity of the foam insulation is not disrupted. Since the insulating layer remains intact, water or other contaminants are prevented from reaching the inner steel pipe, thereby extending the useful life of the pipeline.
An invention has been provided with several advantages. The external slip wrap of the invention alleviates problems previously encountered with high temperature piping systems where elbows and other angled fittings caused the pipe to be subjected to damaging stresses. The system incorporates several existing, commercially available materials or components, thereby simplifying manufacture and assembly. The particular application of the slip wrap of the system compensates for relative movement of the inner steel pipe which could disrupt the continuity of the surrounding insulating layer at an elbow or other fitting. The coupling is simple in design and economical to implement in a variety of industrial applications.
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|US20110041925 *||Aug 19, 2009||Feb 24, 2011||Thermacor Process, Lp||Method of Installing Pre-Insulated Piping|
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|U.S. Classification||138/120, 285/45, 138/155, 285/228, 138/145, 138/118, 138/149, 285/299|
|Cooperative Classification||F16L59/15, F16L59/22|
|European Classification||F16L59/22, F16L59/15|
|Feb 28, 2007||AS||Assignment|
Owner name: THERMACOR PROCESS, L.P., TEXAS
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:KEYES, THOMAS JOSEPH;REEL/FRAME:018940/0372
Effective date: 20070223
|Sep 16, 2011||FPAY||Fee payment|
Year of fee payment: 4
|Oct 14, 2013||AS||Assignment|
Owner name: THERMACOR PROCESS, INC., TEXAS
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:THERMACOR PROCESS, L. P.;REEL/FRAME:031399/0359
Effective date: 20131010
|Sep 23, 2015||FPAY||Fee payment|
Year of fee payment: 8